NITROGLYCERIN INFUSION DURING UPRIGHT TILT - A NEW TEST FOR THE DIAGNOSIS OF VASOVAGAL SYNCOPE

The aim of our present study was to assess the value of nitroglycerin infusion during upright posture as a new provocative test for diagnosi s of vasovagal syncope. To this purpose 40 patients with unexplained s yncope (17 men and 23 women, mean age 47 years) and 25 asymptomatic co ntrol subjects with negative baseline head-up tilt underwent two other tilting tests, one during nitroglycerin infusion and one during isopr oterenol infusion. The protocol of the nitroglycerin test consisted of a maximum of five successive stages of 5 minutes in the supine positi on plus 10 minutes 80-degree upright tilt at progressively increasing infusion rates (increments of 0.86 mu g/kg/hr every stage). During the nitroglycerin test a positive response (syncope in association with s udden hypotension and bradycardia) occurred in 21 (53%) patients with unexplained syncope, an exaggerated response (minor symptoms in associ ation with slowly increasing hypotension alone) occurred in 10 (25%), a negative response in 9 (22%), and drug intolerance in 0. During the isoproterenol test these percentages were 25%, 25%, 32%, and 18%, resp ectively. Only 2 (8%) control subjects had a positive response to nitr oglycerin test and 2 (8%) to isoproterenol test. Thus the nitroglyceri n test seems to be a useful alternative tool for diagnosis of vasovaga l syncope; it is equally specific but more sensitive and feasible than the isoproterenol test.